Currently the demand for higher rate data communication services is increasing at a very high pace. The need for higher data rates is being driven by user applications such as multimedia, large file transfers, heavy World Wide Web usage (i.e., surfing), video conferencing, Internet video telephony, Internet voice telephony and other bandwidth intensive applications. For example, it requires a substantial amount of data to define a high resolution color picture to be displayed on the monitor of a user's personal computer. It takes an even greater amount of data if the picture is to be animated.
At present, conventional analog modems operating over the public switched telephone network (PSTN) in use in most residential settings can transmit data at a rate of 28,800 bps. Analog modems that transmit at 33,600 bps exist but have not gained widespread use due to the time lag until Internet service providers (ISPs) purchase and install faster modem equipment into their infrastructure.
In addition, such data rates are too slow to accommodate heavy multimedia applications. In many applications, the computer user transmits relatively small amounts of information comprising mainly requests for information to a service provider. Thus, a lower speed channel can be utilized to provide the upstream communications between the user and the service provider without noticeable delays.
Currently, much attention is being directed to using once mainly unidirectional analog data transmission systems, such as the community antenna television (CATV) cable system, for bi-directional data communications. It is estimated that there are over 70 million households in the United States that are wired for cable TV. Virtually all the information that enters the home over the cable is in the form of analog television signals. Some subscribers have the ability to send short commands for ordering pay per view or other types of programming. Most set top cable boxes, however, do not provide sufficient upstream channel capacity for practical use by subscribers for data transmission.
Numerous applications for use over the cable are currently being developed. These include, for example, conventional telephony services, digital video, high speed data, various consumer purchasing services, consumer voting services, movie rentals, games, educational courses, travel services, financial services (e.g., stock trading), etc.
Conventional cable transmission systems provide one way transmission from the head-end to the subscriber's residence using a downstream channel in the range of 50 to 860 MHz. In order to satisfy the requirement of interactivity on the information superhighway, cable operators has allocated a reverse channel or upstream channel in the frequency spectrum of 5 to 50 MHz.
Currently, RF to the home is the most common type of broadband service installed with the major service provided being cable television. In addition, the demand for high speed data access from homes and small businesses, i.e., the `on-ramps` to the information highway, is increasing. There is a growing need to provide facility transport between customer premises and the head end location. A facility such as T1 (1.544 Mbps) or E1 (2.048 Mbps) can be used to connect primary multiplexing equipment providing communication services to large businesses.
Communication systems for transmitting data over CATV networks are known in the art. U.S. Pat. No. 5,488,412, issued to Majeti et al., teaches a home controller for receiving signals from the cable television system and utilizing a cable demodulator tuned to the RF frequency of the channel which carries the data information. The cable demodulator demodulates the RF encoded signals into conventional baseband digital form which are transmitted to a frame receiver which decodes frames addressed to individual users. If a frame is addressed to the user (i.e., subscriber), the frame receiver transmits the corresponding data using a transceiver (i.e., Ethernet) to the user's personal computer.
U.S. Pat. No. 5,412,352, issued to Graham, teaches a modulator for data to be transmitted in a reverse or upstream channel in a cable transmission system. The modulator requires a single frequency translation from baseband to a selected RF channel, thus eliminating conventional intermediate frequency (IF) translation. The modulator uses a differential quadrature phase shift keying encoder with transversal finite impulse response (FIR) filters and interpolation filters to connect the phase shift keyed data to a single mixer stage for directly translating the baseband signal to an RF signal in the channel spectrum of 5 to 40 MHz.